Generally, such a flip chip bonding process, which is different from the wire bonding process and the TAB (tape automatic bonding) process, is carried out in such a manner that the bumps for bonding the chip to the substrate are formed in a desired form during a separate step of the semiconductor manufacturing process.
As shown in FIGS. 1A through 1F, the conventional bump forming process comprises a step of sputtering Ti or Cr on an aluminum pad 2 which is formed on a chip 1 so as to form a layer, a step of forming a plating base 3 by depositing Cu or Au on the layer after providing an adhesion thereto, a step of forming photoresists 4 on the plating base 3 to define the size of the bump by the photolithography method, a step of forming a bump 5 by electroplating Pb/Sn or Au, Au/Cu on the space between the photoresists 4, a step of removing the photoresists 4 and the depositions due to the electroplating, and a step of shaping the bump 5 into the desired form by flowing the bump 5 under a hydrogen atmosphere after thermal processes for the bump 5.
In general, bumps for use in the flip chip bonding uses Pb/Sn material.
However, the above described bump forming process is very much complicated, and therefore, it is difficult to apply this process during the assembling process. Accordingly, it is troublesome that the bump forming process has to be carried out in a separate manufacturing process.
Recently, a chip bonding process is processed, where the chip bonding can be carried out during the assembling process as shown in FIGS. 3A through 3F.
As shown in FIG. 2, a wire is passed through a capillary 13 to form a ball 12 on the tip thereof, and the wire is cut with a clamp 14 by a wire ball bump bonding apparatus being used in this process.
As shown in FIG. 3, the process includes: steps b and c of installing an Au wire 22 on the wire ball bump bonding apparatus, and forming an Au ball 23 on an electrode 21a of a chip 21, steps d and e of applying an Ag paste 25 to the Au ball 23 by putting the Au ball 23 into a container 24 filled with the Ag paste 25 and by pulling it out therefrom, and step f of bonding the chip 21 to the substrate 26 downward.
In the above described chip bonding process, there is an advantage that the formation of the Au ball 23 can be formed during the assembling process. However, it still has problems that the Au balls 23 are formed very densely in their intervals, and therefore, when the Ag paste 25 is applied to the Au ball 23, they can be connected to the adjacent Au balls 23. In addition, as the height of bumps is small, it is difficult to apply a suitable Ag paste to the Au ball. It means that an Ag paste on the chip might be connected between the adjacent Au balls 23 as well as between electrodes, and the Ag paste 25 is weak at high temperatures, thereby decreasing the reliability of the product.